The invention relates to a drive device for a windshield wiper having an output gear, a gear cover on which is formed a plastic sleeve that is open toward the output gearwheel, and a park position switch comprising first contacts mounted for rotation and second contacts fixed to the gear cover and in sliding contact with the first contacts, such that the contacts mounted for rotation are connected to the output gear via a driving means.
A drive device of this type is disclosed in German Laid Open Application DE 195 48 824 A1.
Drive devices for windshield wipers have switches that ensure that the motor of the drive device continues to be supplied with current after the driver opens the master switch until the windshield wiper has returned to its initial position, which is also referred to as the park position. Accordingly, the switch is called the park position switch.
The park position switch is conventionally implemented as a switching disk having three concentric, partially interrupted contact tracks. A point-like contact element (contact lug) slides along each track to produce an electrically conductive connection to the contact track. The contact tracks or the switching disk are fixed or connected to the output gearwheel of the output spindle, whereas the contact lugs are fixed to the housing, particularly the gear cover.
In this arrangement, in which one element of the park position switch, typically the contact tracks rotating together with the output gearwheel, is fixed to the output spindle, the following problem occurs:
The windshield wiper blade may be prevented from reaching its park position by external influences, e.g., snow on the windshield. However, because the output spindle continues to be driven by the motor until it reaches an angular position that corresponds to the park position of the wiper blade if movement is unimpeded, the wiper arm and the wiper blade are bent by being braced against the obstruction. As soon as the motor switches off automatically, the tension of the wiper is released, so that the output spindle reverses. As a consequence, the park position switch is closed again and the motor is supplied with current. This has the result that the wiper is again driven against the obstacle and mechanical tension builds again. This process is repeated until the obstacle is removed. This obviously causes substantial loading of the gear and thereby reduces the life of the gear.
To solve this problem, the generic drive device is equipped with a snow load safety mechanism, i.e., the park position switch has a supplementary driving means, so that the contacts mounted for rotation are no longer fixed to the output gearwheel but are connected to it via a coupling. This coupling is configured in such a way that the output spindle carries the switching disk along in normal operation, when the wiper is moved back and forth, so that the park position switch works like a park position switch whose switching disk is fixed to the drive spindle. In the above-described case, however, where the drive spindle is reset against its actual direction of rotation, even by the force of the wind, for example, the switching disk is not carried along, so that the park position switch, which would otherwise again supply the motor with current, is not closed.
To obtain a flat construction in connection with a driving means of this type, the aforementioned laid open application furthermore proposes that the contact element mounted for rotation be supported on a plastic sleeve formed on the gear cover and that the drive spindle extend into this sleeve.
Accordingly, from the driving means perspective alone, the contact lugs in the generic device, preferably in the embodiments with rotatable contact paths, could also be mounted for rotation. All the prior-art drive devices have in common, however, that in each case a first plane or contact disk mounted for rotation results, which is in sliding contact with a second, parallel contact plane typically formed by a flat part of the inside of the gear cover. This conventional parallel configuration places significant limits on the design and is also not fully satisfactory in other respects.